The objective of the proposed research is an elucidation of how vagal afferent impulses interact with respiratory centers in the brain stem to establish the frequency and depth of a respiratory cycle in order to produce adequate pulmonary ventilation under various conditions. Transient and steady-state responses to vagal blockade produced by cooling a short segment of one nerve, while the contralateral nerve is cut will be measured during hypoxia, hypercapnia, asphyxia, hypotension, and hypertension. Similar experiments will be performed with the carotid chemoreceptors intact and following chemoreceptor denervation. Transient and steady-state responses will be analyzed to determine the rate at which various cycle parameters respond to an alteration of the various conditions with and without vagal afferent input. The effects of vagal impulses at various times in the respiratory cycle will be studied by anodal block of vagal conduction. This technique, shown to produce immediate block of nerve conduction, reveals the effects of sudden withdrawal of feed-back information from the lungs on the characteristics of the phase of the cycle in which it is applied and on subsequent phases of the cycle.